Pulping cellulose material with an alkaline cooking liquor containing hydrazine



United States Patent PUMPING CELLULQSE MATERIAL WETH AN ALKALENE (JGQKHNG LKQUUR CUNTAHQ- DIG HYDRAZINE Athey G. Gillaspie, Hamilton, Ohio, assignor to Champion Papers line, a corporation of Ohio No Drawing. Filed Dec. 13, 1060, Ser. No. 75,476

9 Claims. Cl. 16272) This invention relates to a method of producing cellulosic pulp such as wood pulp by the digestion of lignocellulosic materials with alkaline pulping liquors. In particular, it relates to the cooking of such materials in the presence of an agent which apparently inhibits the consumption of the alkaline reagents in those reactions in the pulping process which consume alkali without solubilizing lignin, thereby making the alkaline reagents more effective pulping materials.

In the conventional pulping processes a charge of lignocellulosic material, such as wood chips, straw, bamboo chips, or the like, is digested in a closed vessel at an elevated temperature in the range of about 300 to 370 F. and at corresponding pressures, usually in the range of 66 to 172 pounds per square inch. The alkaline process, as its name implies, is carried out at an alkaline pH. Sodium hydroxide may be the sole pulping agent present, as in the so-called soda process. Mixtures of sodium hydroxide and sodium sulfide together with a certain amount of sodium carbonate are employed in the krat't orsulfate process. Between 30 and 90 grams per liter of these agents, calculated as Na O, are normally employed; expressed another way, the amount of active reagent in the liquor is usually between to and most often between 16% and 18%, calculated as Na O, on the dry weight of the lignocellulosic material, for the production of pulps which are to be bleached.

In the various alkaline pulping processes and modifications thereof, the combination of the high alkalinity and elevated temperatures and pressures employed in the digestion, have certain deleterious effects that are more or less accepted as necessary evils. Although the lignin is converted into removable form and the cellulose fibers are liberated, at the same time under these severe conditions, certain desirable materials such as the hemi-celluloses are dissolved and thereby lost, the lignin degradation products present in the wood and wood pulping medium are partially transformed into dark color-bodies which impair the color of the cellulose, and the cellulose chains are to some extent hydrolyzed or broken. As a result more material is removed than is necessary and the yield is low, in the range of 43% to 48% bleachable pulp on the weight of the wood used. If the cooking were less drastic, less of the hemi-cellulose would be removed and less of the smaller molecule carbohydrates would be split into the shorter chain lengths, and as a result, higher yields of pulp could be obtained. It should be possible in the case of fully cooked pulps to increase yields to 50% to 60% after pulping and still have a pulp of comparable strength and appearance. Retention of more of the hemicellulose would be advantageous as such material aids in the beating of. the pulp and development of strength properties of the paper. Furthermore if the pulping could be modified to lessen or avoid the formation of color-bodies,

the fibers should be easier to bleach. Moreover, if less severe conditions could be employed, a decided improvement in the strength of the pulp could be achieved; there would be less degradation of the cellulose, with better chain length as shown by higher disperse-viscosity values.

While it is known that mild cooking can be secured by reducing the caustic content, this ordinarily must be compensated by a substantially increased cooking cycle. In a ice commercial operation it is not desirable for economic reasons to increase the cooking time unnecessarily.

An object of this invention is therefore an improved method of pulping cellulosic material such as wood pulp.

Another object of this invention is an improved process of pulping coniferous woods.

Still another object of this invention is a pulping process for lignocellulosic materials which requires a significantly reduced amount of alkali.

A further object of this invention is a pulping process for lignocellulosic materials which results in an increased yield of pulp.

An additional object of this invention is a method of producing a pulp of superior properties.

Other objects of this invention will be apparent from the disclosure herein.

In accordance with this invention it has been found that an addition of hydrazine to alkaline pulping liquors in certain proportions significantly increases the yield of delignified fibers and in addition produces a pulp of unusually high viscosity and improved brightness. By replacing a portion of the conventional pulping alkali reagents with hydrazine the less drastic cooking conditions result in less removal of the hemicellulose and less splitting of the smaller molecule carbohydrates.

While it is not completely understood why the use of hydrazine in an alkaline digestion liquor results in a greatly improved pulping process, it is believed to be due to the afiinity of hydrazine for carbonyl groups in the cellulose. This afiinity results in stabilization of the cellulose in such a manner as to make the caustic selective in its action against the lignin. Apparently the hydrazine causes the alkali to first react with the lignin and other readily removable materials, leaving the cellulose and hemicellulose intact. In this regard it has been established by experimentation with a fully bleached pulp that hydrazine does not prevent alkali from attacking cellulose; because of this it appears to subdue such action until all of the non-cellulosic or more readily reactive materials present in the chips are dissolved. While it is recognized that a number of reducing agents have been suggested in the literature as a means to facilitate pulping, none of these afford as significant a modification in regard to both yield and pulp properties as is obtained by the use of hydrazine. For this reason it appears that the action of hydrazine is an alkaline pulping system is not merely due to its reducing properties alone.

The hydrazine and alkali must be employed in certain proportions in the pulping liquor in order to obtain a beneficial digestion of the pulp. If hydrazine is employed in a full strength pulping liquor containing the usual 15 to 20% active alkali, calculated as Na O, and based on the dry weight of the wood, the full shielding eifect of the carbonyl groups by the hydrazine is not realized. For this reason the hydrazine is ordinarily effective only when no more than about 13% of active alkali calculated as N320, and based on the dry weight of the wood is used. It has been found that a maximum yield of a pulp of the most desirable properties is ordinarily obtained when the Na O content does not exceed 10%. Since the wood chips are not defibered fully when less than 7% of alkali is employed it will usually be desirable to work within the particularly effective range of 7% to 10% alkali. If a semi-chemical pulping is desired it is possible to use 3% to 7% alkali followed by a mechanical defibering operation. The hydrazine will ordinarily be employed in the range of 12% to 30% based on the dry weight of the wood chips. Amounts in excess of 30% such as up to 40%, usually provide little or no additional benefit. Moreover, below 12% of hydrazine there is a gradual failure to completely shield the cellulose a) from the caustic. Below 8%, the hydrazine has little or no effect.

The pulping liquor will contain water, the conventional alkali and other ingredients in addition to hydrazine considered a constituent of the liquor when expressing ratios of liquor to chips.

A further advantage of the process of this invention is improved quality of the pulp in regard to the amount In conventional digestion and the wood chips. Sodium hydroxide, being readily 5 of agent required to bleach it. available, is the preferred alkali although other alkali of wood chips, the cooking is carried to a point where metal hydroxides such as potassium hydroxide may also the yield of pulp, basis dry wood before bleaching, is be employed. Sodium sulfide and other sulfides will be etween 43-48%, and the permanganate number (P.N.) present in the liquor used in the sulfate process. Inert is between 16 and 20 for softwoods. The P.N. is an ingredients which are ordinarily present in the cooking indication of the oxygen demand of the unbleached pulp or white liquor used in the sulfate process are sodium (brown stock) which, in turn, is an indication of the carbonate, sodium sulfate, sodium sulfite, etc. The amount of lignin and other reducing material left on the hydrazine hydrates can be used in place of hydrazine fibers that must be removed by the bleaching operation. provided the amount of NH NH present for the reaction In other Words, the higher the P.N. number the greater is within the amount specified. amount of chlorine (and other bleaching agents) needed.

The yield of pulp produced with the alkali hydrazine The P.N. is not strictly quantitative but is merely an indiliquors in accordance with this invention is generally in cation for any one pulping or bleaching system. the range of 50% to 56% and occasionally as high as Pulps produced in accordance with this invention gen- 60%, based on the initial amount of wood chips, or about erally have P.N. values which are slightly lower than 10% to 15% higher than that obtained with a conventhose produced by a conventional operation. Moreover, tional kraft liquor. The increased yield of pulp and a pulp produced by this invention actually bleaches much the need for using substantially less than the conventional InOffl easily than a Conventional Kraft P which has a amount of alkali results in a highly efficient process. similar P.N.; i.e., a brightness of 80 can usually be The method of this invention is particularly useful obtained in four stages instead of the normal five or six with coniferous woods, especially pines, since these prestages. The hydrazine pulps are therefore characterized sent a much greater problem in pulping to obtain a high by ease of bleaching. yield of a product of desirable properties. There is Still another imp feature of the hydfaline P 1 generally much less difficulty with the hardwoods in ing process is that the strength of the pulp is not maobtaining high yields having desirable P.N. values and terially lowered as it is in a conventional pulping opercorrespondingly suitable viscosities. ation. A measure of the strength of pulp is the Cupri- Since the pines are normally pulped by the kraft or ethylenediamine Disperse Viscosity of Pulp, TAPPI sulfate process using a mixture of sodium hydroxide and standard T-230mm-50. This disperse viscosity is a sodium sulfide, the hydrazine is particularly useful theremeasure of the chain length of the cellulose molecules with. A further reason for the use of sodium sulfide is present in the fibers, and is an indication of the amount that it serves as a poison for ions that might otherwise of degradation due, initially, to the pulping operation, catalyze the dangerous and explosive decomposition of and later to the bleaching operations. The superior vishydrazine in an alkaline system. cosity of the hydrazine pulp is reflected in better mullen The conditions of the pulping process, other than the and fold values before bleaching and partial development reduced alkali content, are generally the same as employed of these properties immediately upon bleaching. in the conventional pulping operations. Ordinarily the Brightness values given herein were measured on a presence of hydrazine permits the use of temperatures General Electric brightness meter. and pressures which are somewhat lower than the normal The following examples will serve to further illustrate range of about 300 to 370 F. and 66 to 172 pounds per the invention. square inch. Even with hydrazine the use of tempera- Example I tures and pressures much below the minimum of these ranges results in an incomplete removal of lignin. Where A sample of mixed pine chips is pulped by the Kraft only a partial cooking is required, however, less drastic Process (using sodium hydroxide and sodium sulfide as conditions can be employed. The ratio of the alkaline the active alkali) as follows:

Active Sulfidity NH NH; Yield of Chips, NBZOQJGI- (percent Content P111!) (P Sarnple Ovcn dry cent by by wt. Activity Liquor: (percent cent based P.N. Viscosity Bright- Weight wt. based based on Chips by wt. on 011 OD ness (Grams) 0n chips) total dry wt. chips) alkali) chips) Control 2,000 16 2s 88 3.711 0 45.3 15.7 17.8 20.4 2,000 8 2s 88 am 30 54.3 14.3 38.3 38.0

hydrazine liquor to cellulosic material such as wood chips The samples are pulped in a closed digester at 350 should be within the normal range of about 3:1 to 5:1. F. for 100 minutes after taking minutes to attain this The sulfidity content of kraft pulping liquors should 60 temperature. It is observed that the sample containing ordinarily not exceed 40% by weight based on the total hydrazine generated slightly greater pressure than that alkali and most often should be in the range of 15% containing no hydrazine. to 35%. It can be seen from this example that the use of The standard terms used herein to designate chernhydrazine at reduced Na O content provides nearly a icals in a cook are those defined by the Technical 10% increase in yield although pulping to substantially Association of the Pulp and Paper Industry. The total the same hardness, i.e., about 15. In addition the hychemical in a cook is the weight of all sodium salts drazine pulp has a much greater brightness and viscosity expressed as Na O. The total alkali is the weight of than the control sample pulped in the absence of hy- NaOH+Na S+Na CO +Na SO all expressed as Na O. drazine. The active alkali is the weight of NaOH+Na S given as The unbleached hydrazine pulp of Sample I actually Na O. Activity equals the weight of active alkali divided requires a lesser period of ball milling or hydration in by the weight of titratable alkali (NaOH-FNa CO +Na S order to obtain a pulp having the most suitable mullen, all expressed as Na O). The sulfidity is the weight of tear and fold than does the Control or conventional pulp. sulfide expressed as Na O divided by the weight total At this shorter period of hydration the respective propertitratable alkali. As employed herein, the hydrazine is ties of the hydrazine pulp are equal to or superior to Example 111 This example illustrates the effect of variations of the hydrazine and chemical contents (NaOH-I-Na S) of several cooks. All samples are cooked at a 4:1 liquor to chip ratio for a period of 60 minutes to attain 350 F. and then a period of 100 minutes at 350 F. The wood is again a chipped southern pine.

Active NaiO, percent by wt. based on chips Sulfidity, percent by wt. based on total alkali NH2NH3 content, percent by wt. on dry wt. chips Final pH Sample Activity, of Liquor Percent Screened, percent on 0.1).

Yield Yield Total, percent based on O.D.

chips P.N. Viscosity Remarks chips VII* Normal pulping operation.

Use of all sulfide results in no pulping at this level.

Use of very low alkali content results in mere softening of chips and very little pulping. Essentially a semichemical pulp. The softened chips were defibered mechanically in a disc refiner by a single pass using stainless steel surfaces at a clearance of less than about 0.0001 inch.

Good results using hydrazine with reduced alkali content.

Inadequate pulping because of insufiicient hydrazine at this alkali content. About 7% does not pass through screen.

Good product although yield not as high as when greater amount of hydrazine used.

Yield greatly increased with amount of hydrazine in spite of shorter cooking cycle.

* This sample cooked at 350 F. for only 60 minutes.

ide extraction, and (6) 4% calcium hypochlorite the following results were obtained:

From the above it will be seen that the bleached hydrazine pulp resulted in a much higher brightness and viscosity than the conventional pulp bleached by the same sequence.

Having thus disclosed the invention it will be apparent that various modifications thereof may be made which appear within the spirit of the invention and the scope of the claims.

I claim:

1. The method of producing a cellulosic pulp which comprises cooking a cellulosic material with an aqueous alkaline cooking liquor containing an amount of hydrazine which is at least about 8% by weight based on the dry weight of the cellulosic material.

2. The method of claim 1 wherein the aqueous alkaline cooking liquor contains no more than about 13% active alkali, calculated as Na O and based on the dry weight of the cellulosic material.

Example 11 Active NH NH Pressure Full Yield Chips, Na O (per- Activity, Content Raising Pressure Total, Sample Oven Dry cent by Percent (percent Period, Period, Appearance of Pulp percent by P.N. Viscosity Weight wt. based (approx.) by wt. on Min. To Min. At wt. based on chips) dry wt. 350 F. 350 F on chips chips) Control A* 50 0 0 12. 8 40 100 Bright-Unpulped. Control B 2, 000 20 100 0 100 Light Brown 24. 8 29. 5 11.3 1* 50 10 100 19. 2 45 100 Light 52. 6 18. 8 21. 6

* As a safety factor, these were performed in a bomb reactor.

Control A shows that hydrazine in the absence of alkali does not facilitate pulping. Control B shows a normal soda pulping with a characteristic low viscosity and poor yield. In Sample I a pulp is obtained in an increased yield with an excellent P.N. and viscosity yet I only half the normal amount of alkali has been employed.

While the eifect of hydrazine is not as significant in the absence of sulfide, nevertheless it is apparent that the efiiciency of the pulping is increased by its presence.

7 8 to 30% by weight of hydrazine, based on the dry weight 9. The product produced by the method of claim 5. of the chips.

6. The method according to claim 5 wherein the said References Cited in the file of this Patent liquor has a sulfidity content of 15% to 40%.

UNITED STATES PATENTS 7. The method according to clalm 5 wherein the said 5 wood chips are coniferous wood chips. g g S g 8. Method according to claim 5 wherein the said liquor 5 6 am et a c Contains 7% to 10% active alkali, calculated as N 0 7 Hartler July 1962 and based on the dry weight of the chips, and 12% to FOREIGN PATENTS 30% hydrazine, based on the dry weight of the wood 10 846 079 Great Britain g 24 1960 chips.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,l6l ,562 December 15, 1964 Athey G. Gillaspie It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as c arrected below k Column 2, line 46, for "is an" read in an line 56,

after "alkali" insert a comma; column 4, line 57, for "pulp" read pulps line 46, for "Kraft" read kraft columns S and 6, Example III chart, seventh column, in the headingafter "percent" insert based same chart, last column, opposite Sample VII", after "with" insert greater same columns 5 and 6, Example ll chart, column 9, line 2 thereof for "2408" read 42.8

Signed and sealed this 13th day of July 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attnsting Officer Commissioner of Patents 

1. THE METHOD OF PRODUCING A CELLULOSIC PULP WHICH COMPRISES COLLING A CELLULOSIC MATERIAL WITH AN AQUEOUS ALKALINE COOKING LIQUOR CONTAINING AN AMOUNT OF HYDRAZINE WHICH IS AT LEAST ABOUT 8% BY WEIGHT BASED ON THE DRY WEIGHT OF THE CELLULOSIC MATERIAL. 